The modern battlefield requires new and innovative tactical vehicle technologies to address challenges whose emergence has been seen with dramatic effect in both Iraq and Afghanistan. Among these, personnel protection and fuel economy ranks at the top of the list.
In many ways personnel protection and fuel economy go hand-in-hand. Increase the amount of armor on a vehicle to improve personnel protection and you increase the weight of the vehicle and you decrease its fuel economy. Increase a vehicles' fuel economy by reducing its engine's horsepower and you degrade its performance and decrease a soldier's ability to get out of harms way. While these are the most obvious components of the conundrum, several other issues emerge upon further inspection. For example, completely armoring a vehicle now means that its cabin's environment must be continuously heated or cooled to maintain comfort for its occupants. The heating and/or cooling, depending on the outside ambient temperature, reduce the vehicles fuel economy. This reduction in economy is a result of not only the horsepower required for its operation but also the weight that its components add to the vehicle.
Fully armored tactical vehicles not only enclose the crew compartment but also that of the engine. In typical applications the vehicles' air conditioning condenser is installed just ahead of the engines' charge air cooler which is mounted just ahead of the engines' radiator. This “stacking” of coolers results in the over sizing of components in order to compensate for the successive reduction in air flow and increase in effective ambient temperature. Additionally, after the air has flowed through these cooler assemblies it must now find its way out of the enclosed space, creating a positive back pressure within the engine compartment.
Optimizing vehicle systems such as cabin climate control cannot be done without a “Total Vehicle” approach. Air Conditioning and Heating Systems are generally not “add-ons” that are installed after a vehicle is designed. Integration from vehicle conception is the key to reaching the new goals dictated by today's battlefield environment.
The Modern Military Vehicles that are being designed must maximize available horsepower. With the installation of a conventional air conditioning system, air must be blown across the condenser to disperse heat contained in the R134A. Because of the design of the vehicle, the front grill has heavy armor with small vents to prevent as much damage as possible caused by explosions. Air is pulled into the engine compartment by a fan and then travels through the engine radiator to cool the water/glycol and then to the air conditioner condenser to cool the R134A refrigerant.
It is very important that the Modern Military Vehicle be such that it can be serviced and maintained as quickly as possible. If the vehicle becomes disabled and requires the replacement of an engine, every effort has been made to make this as easy as possible. Where a conventional air conditioning system is installed and a new engine is required, the entire air conditioning system must be removed. Once a new engine is installed the air conditioning system must be re-installed and re-charged with R134A. This process adds time and labor to the process.
A conventional air conditioning system requires refrigerant lines to run from the engine compartment to the crew cabin and back, requiring two penetrations in the hull of the vehicle. This creates three problems in the Modern Military Vehicle. One, the length of the refrigerant lines required making this loop, two, the amount of R134A required to keep the system charged, and three, two penetrations are required for the line to enter the hull and return to the engine compartment. The longer the refrigerant line, the higher the risk of leakage. When the system is down it takes costly time and labor to repair. If more R134A is required for the system, created in part by the length of the line, more refrigerant must be transported and inventoried to maintain adequate supply. Finally, each penetration that is bored into the hull of the vehicle increases the danger to the cabin crew by providing a path for foreign objects or materials to enter.
Another issue with a conventional air conditioning system is that the compressor speed is directly proportional to the speed of the engine. This means that the compressor must operate in either an “off” or “on” mode to control temperature thereby reducing the efficiency of the compressor.
Accordingly, there is a need for an air conditioning system that, among other things, is more efficient and easy to install or remove than conventional air conditioning systems.